A Review of Criticality Accidents A Review of Criticality Accidents

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90 Support Hydraulic Lift Rail Track Lower Assembly Pipe Cart 200 mm 1.84 meter 1 meter Neutron Detectors Control Room FKBN–2M FKBN–2M Control Panel Figure 54. FKBN-2M building layout. Figure 55. FKBN-2M experimental layout. Upper Assembly Ring Support Lower Support Horizontal Motion Carriage
completed the construction of the lower half of the assembly on the table (Figure 56). This lower half consisted of the copper reflector (with an outside diameter of 258 mm since that was all that was available) and a uranium core (9 spherical layers, with an inside diameter of 28 mm and an outside diameter of 167 mm) with a neutron source (~10 5 n/s) placed in its center. As he went to position the first upper copper hemishell (with an inside and outside diameters of 167 mm and 183 mm, respectively) into place it dropped onto the bottom assembly. This led to the initial prompt critical spike and the ~6.5 day excursion. The automatic scram system activated and dropped the table to its down position 60 but otherwise had no effect on the supercritical assembly. After the initial fission burst, the assembly eventually reached steady state power conditions. Seeing a flash of light, the experimenter left the experimental cell, shutting the safety door behind him. He reported the accident to the engineer and attending health physicist who were in the control room at the time. The head of the laboratory and the facility chief were then notified by phone. The facility chief arrived shortly thereafter, at which time the experimenter related the composition and dimensions of the assembly as documented in his logbook. 60 The accident burst conditions were reproduced from measurement of the assembly’s neutron flux (19 June 1997) and from computations shown in Figure 57 Support Core (HEU) Reflector (copper) Neutron Source Figure 56. Accident configuration. (these computations were performed by Dr. V. F. Kolesov and Dr. V. Kh. Khoruzhy). The asymptotic power was estimated to be 480 watts, corresponding to an event with an initial excess reactivity 6.5 ¢ above prompt critical, i.e., ∆k = 0.00745. The initial superprompt critical spike of ~4 × 10 15 fissions was followed by a subprompt critical excursion lasting 3 to 5 minutes and generating ~2 × 10 17 fissions. This second excursion was followed by highly damped power oscillations separated by about 40 minute intervals. Several hours afterwards, the assembly power, and the core and reflector temperatures had reached equilibrium levels. The temperature of the uranium core was estimated to have been 865°C. The excursion was terminated around 00:45 on 24 June 1997 when a vacuum gripper was used to remove most of the assembly from the stand, leaving only the outermost lower copper hemishell in place. The removed portion of the assembly was placed onto a support stand in the room (Figure 58). All the recovery operations were done remotely. Later, another two hemishells from the lower reflector were removed, and the system was then separated into two parts and packaged into containers. After the γ-radiation decreased to allowable levels, it was planned to further disassemble the system (into single components) to restore the damaged coppernickel protective coating on fissile material parts. Ring Assembly Support Support Pipe Lower Support Hydraulic Lift Carriage Cart 91
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LA-13638 Approved for public releas
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A Review of Criticality Accidents 2
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PREFACE This document is the second
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Tom Jones was invaluable in generat
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C. OBSERVATIONS AND LESSONS LEARNED
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FIGURES 1. Chronology of process cr
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51. MSKS and assembly involved in t
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A REVIEW OF CRITICALITY ACCIDENTS A
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3 Black Sea Baltic Sea Obninsk Norw
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North Atlantic Ocean Irish Sea Wind
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1. Mayak Production Association, 15
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time of the accident. However, the
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determined by a radiation control p
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consequences of this accident, the
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Figure 10. Drum in which the 1958 Y
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The entire plutonium process area h
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During the next shift, radiation sa
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9. Siberian Chemical Combine, 14 Ju
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The accident investigation determin
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10. Hanford Works, 7 April 1962 18,
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heater and stirrer were turned off
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vessel 64-A was added. The dissolut
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additional reflection afforded by t
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15. Electrostal Machine Building Pl
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Page 53 and 54: ased on a radiation survey, that th
Page 55 and 56: 0.5 m 0.5 m 0.5 m 0.5 m 3.0 m 1.4 m
Page 57 and 58: The investigation identified severa
Page 59 and 60: 19. Idaho Chemical Processing Plant
Page 61 and 62: 20. Siberian Chemical Combine, 13 D
Page 63 and 64: To Glovebox 6 7 8 6 From Glovebox 6
Page 65 and 66: on a 0.4 m square pitch grid. The b
Page 67 and 68: competing reactivity effects proved
Page 69 and 70: Figure 35. The precipitation vessel
Page 71 and 72: B. PHYSICAL AND NEUTRONIC CHARACTER
Page 73 and 74: Material Fissile Mass: Fissile mass
Page 75 and 76: 235 U Spherical Critical Mass (kg)
Page 77 and 78: Table 10. Accident Fission Energy R
Page 79 and 80: • Accidents in shielded facilitie
Page 81 and 82: • Senior management should be awa
Page 83 and 84: Table 11. Reactor and Critical Expe
Page 85 and 86: 3. Oak Ridge National Laboratory, 2
Page 87 and 88: 5. Oak Ridge National Laboratory, 3
Page 89 and 90: eflector of 236 kg when he noticed
Page 91 and 92: 3. Los Alamos Scientific Laboratory
Page 93 and 94: At the equatorial plane, the two ha
Page 95 and 96: Figure 48. The Los Alamos Scientifi
Page 97 and 98: Figure 50. Burst rod and several se
Page 99 and 100: On 11 March 1963, the facility chie
Page 101 and 102: 13. Chelyabinsk-70, 5 April 1968 57
Page 103: 14. Aberdeen Proving Ground, 6 Sept
Page 107 and 108: C. MODERATED METAL OR OXIDE SYSTEMS
Page 109 and 110: 63,65,66, 67 4. Chalk River Laborat
Page 111 and 112: 7. Centre dÉtudes Nucleaires de Sa
Page 113 and 114: a technician prescribing the loadin
Page 115 and 116: the room to drain the water out of
Page 117 and 118: In the final experiment, the critic
Page 121 and 122: III. POWER EXCURSIONS AND QUENCHING
Page 123 and 124: Figure 64. Energy model computation
Page 125 and 126: References 1. Stratton, W. R. A Rev
Page 127 and 128: 50. Paxton, H. C. “Godiva Wrecked
Page 129 and 130: 92. Stone, R. S., H. P. Sleeper, Jr
Page 131 and 132: criticality accident: The release o
Page 133 and 134: prompt criticality: State of a fiss
Page 135 and 136: 1. Mayak Production Association, 15
Page 143 and 144: 9. Siberian Chemical Combine (Tomsk
Page 147 and 148: 13. Siberian Chemical Combine, 2 De
Page 149 and 150: 15. Electrostal Machine Building Pl
Page 153 and 154: 19. Idaho Chemical Processing Plant
Page 155 and 156:
21. Novosibirsk Chemical Concentrat
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